In the field of telecommunications, particularly in connection with the implementation of long distance networks, there is continuing pressure to increase the traffic carrying capability of the transmission media. For example, since fiber optic cables can carry large numbers of circuits, they are used increasingly for connecting network stations and other network elements. One result of this compaction is that an outage due to a fiber cable break, for example, can cause massive disruption of services to a large number of network customers and users. The ability to quickly and economically restore traffic affected by these outages is therefore of considerable benefit. Restoring the highest value, highest priority circuits first, and as many circuits as possible for a complex network is a difficult problem to say the least, and efficient, workable solutions, appropriate for today's high capacity networks are being sought.
Despite the trend to high capacity media and the capabilities of fiber optics in that regard, there has not been an immediate, sweeping implementation of fiber optical systems. Although the reasons for that are not especially relevant here, one result has been that current networks are generally hybrid in nature and older technologies are used in combination with emerging technologies. Thus, in dealing with restoral problems it is desirable that the solutions be independent of the technology used in the network.
Heretofore, to deal with the problem of network outages, one of the techniques used was to simulate different failure scenarios in advance and to establish from those scenarios appropriate instructions (or preplans) that could be used at stations of the network to establish restoral routes to recover from the outage. Since the number of failures possible in a network can be very large it is not always practical to have instructions or a plan for every scenario. Furthermore, since technological improvements allow network topologies to be changed relatively quickly and easily, long distance networks are not as static as in the past and preplans for restoration quickly become outdated.
It has become essential therefore to quickly determine and implement alternate routes for the impacted circuits on the network topology as it remains.
On one hand, large numbers of routes need to be determined with limited resources; on the other hand, routes need to be restored in near real time to maintain reliable communications.
It is therefore among the objectives of the present invention to provide a method for quickly restoring routes between network stations (or nodes) following a disruption of service due to circuit outages such as those that result from a cable break between stations. Further, it is sought to provide such a method which will be independent of the transmission technologies used in the network and which will assure that routes of highest priority will be restored in preference to those of lower priority, preferably taking into account the relative costs of alternate routing.